1. Field of the Disclosure
The present disclosure relates to electronic devices, more particularly, to electronic devices that have electrodes including barrier layers and processes for forming them.
2. Description of the Related Art
A low resistance electrical connection with high physical strength between a substrate and a package is important in electronic devices, especially those that are designed to operate at relatively high power or current conditions. A barrier layer of titanium, followed by a solderable layer of nickel or nickel vanadium, further followed by an oxidation-resistant layer of gold are added to the back of the substrate to form an electrode to lower the resistance of the connection between the substrate and the package.
However, insulating material, such as a native oxide or other residual material from previous processing lying between the back of the substrate and the barrier layer can cause unacceptably high resistance between the substrate and the package. One attempt to improve the electrical connection is to sputter etch the back of the substrate with argon to remove any such layers prior to forming the electrode. Removing the insulating material using argon can improve the electrical connection, but the physical connection between the metal layer and the substrate can be compromised such that the electrode would peel during a conventional tape test.
One attempt to improve the physical connection is to vent the chamber to atmosphere so that a native oxide forms on the substrate and acts as an adhesion layer for the electrode. The native oxide can also increase the resistance between the substrate and the package. Forming the native oxide layer can also require that a subsequent process step be performed at a temperature of 380 C or higher, such as when a die previously singulated from the substrate is mounted on the package. Another attempt is to bake the substrate after the sputter-etch at a temperature of about 380 C or greater prior to forming the barrier layer of the electrode. This may not be practical in a piece of etch or deposition equipment that is not factory-equipped with heat control in the deposition chamber. Replacement of such a piece of etch or deposition equipment is expensive and may require requalification of existing products.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments described herein. The use of the same reference symbols in different drawings indicates similar or identical items.